Safety fuse



Sept. 29, 1931.

By tlorneys,

Patented Sept. 29, 1931 narran stares rarsnrerrics 't HENRY E.ELLSWORTH, OF SIMSBUEY, CONNECTICUT, ASSIGNOR T THE y ENSIGN- BICKFORDCO., OF SIIVISBURY, CONNECTICUT, A CORPORATION' OF CONNECTICUT."

SAFETY FUSE Application filed February 28, 1930. Serial No.l 432,086.

The present invention relates to safety fuse, to products made from orembodying such fuse and to the manner of using ther same.

,- An object of the invention is to provide a new and improved type ofweatherproof safety fuse. A further object is to provide safety fusewhich may be readily primed with a composition to assist in the easyignition of the fuse. A still further object is to provide a very slowburning fuse of unliform burning rate. A still further Objectis toemploy such fuse cut into short lengths as delay elements for use inelectric blasting 15 caps, which delay elements may be vprimed at oneend if desired.

According to th-e present invention I accomplish the foregoing and otherobjects by pioviding safety fuse consisting of a core 2g of inflammablematerial enclosed Within a fibrous or cellular covering, and theresulting fuse enclosed within a covering of impervious material'.APreferably the inflammable material is a slow burning powder;

the fibrous covering, a textile which is woven or wrapped around thepowder core; the covering of impervious material, a metal such as lead,tin, aluminum or the like,

' which is closely fitted over the textile mate- ,30 rial to reduce to aminimum or` entirely eliminate air spaces between thebutside of thetextile covering and the inside of the metallic covering. This fuse canbe used in the conventional manner or it may be cut into short lengthsand primed with an easily ignitable compound to provide delay elementsfor velectric blasting caps. Y

The invention will be better understood from the detailed descriptionwhich follows e0 and the accompanying drawings, wherein Figure l is alongitudinal, diametrical section through a. portion of safety fuseembodying the present invention.

Fig. 2 is a transverse section of the safety fuse taken substantiallyalong the plane of the line 2 2 of Fig. 1.

Fig. 3 is an elevation partly broken away of an application of thesafetyV fuse of the present invention to form what is termed a delayelement.

.Fig 4l is a longitudinal, diainetrical section of an electric blastingcap Vwhich embodies a delay'element shown' in Fig. 3.

Referring first to Figs. l and 2 of4 the drawings, the safety-fuseconsists of alcore A of slow burning powder which is enclosed in awrapping orcovering Bof textile.

fabric preferably formed ofjute and cotton yarns. The elements A and Binassembled relation constitute what is recognized'in the arts as safetyfuse, and the composition of the powder A and the character ofthecovering B may be varied, as desired. Snugly engaging around thecovering B is artube Cv of impervious material which is of a relativelynon-conibustible character, and one that is capable of having its outerdiameter accurately sized for a pur-pose which will presently bemadeapparent. Preferably this outer tube Ais formed of lead, but it will beunderstood -that yit may be formed of other ductile metals or any othersubstance which may be found to have the requisite characteristics. n

Thesafety fuse A, B, C may be fabricated or manufactured in any mannerwhich is.

found practicable, it being a desirable quality of the fuse that thecoating C closely engage the covering B -so that air spaces between saidB and C will be reduced to a minimum or entirely eliminated. It is alsodesirable that the covering B be formed .of a textile which hasacellular structure so trat airmay be occluded within said cells orbetween the fibers of the textile material, so that as the powder coreburns, the air cells will provide a cooling andY insulating effect whichwill prevent the melting of the outer coating C, which melting mightresult in obstructing the propagation yof the burning.

in the production of the-safetyA fuse A, B, C, a powder core A of asuitably slow and uniform burning powder is spun into fuse A, B, by aprocess similar to that used in making resin-core solder, lead coveredcables and the like.

In Fig. 3 there is illustrated what I term a delay element for electricblasting caps, said delay element being formed of a suitable length lofsafety fuse, asiillustrated in Fig. l, which pieceof fuse, after beingcut to the desired length, and accurately `sized to suitable diameteritisprimed at one end, as shownatD, with 'an easily igiiitable'compound. Theprimin'g compound may be of any desired or preferredcompositionfand I have found as a suitable composition foi this purposea paste gfoi'ined-by dissolving' Celluloid in acetone and mixingtherewith ordinary' blacky meal 'powdeiU in the proportion :of twentypa'rtsfby weight of powder to oneipart of Celluloid. `A vdelay elementsuoli 'as above described should `iliave the following specilications:

ELS

meltl during burning.

`l. Itmustburii very slowl'yian'd accurate ly-`-in fact, morefslowlyfan'd with Vgreater accuracy' than 'any' safety? fuse? hithertomade for-general use.` f

V52,. AIt must have a uniform and `accurate diameter.

B. It musthave a rigid body which can bezp'ressed into a copper shell,producing a veryclose iit, so that -the ila'sh from the igniter cannotpass between the F fuse element and the' copper tube and Aprodiitey apremature' ignition. The importance of this feature will be *appreciatedwhen one considers-that the 'shortest'elements are only i aboutone-quarter inch longuaii'd'vthe igniter produces' a veryV4 hot andsudden-flash.

4. It must be easily ignited.

5. It must burn without emission of side sparks or hot gases.

6. 'The metal tubemust Vnot ruptureor '7. 'It shouldbelch'eapf and easytolmanufacture.

The delay element as shown in Fig'. 3, and having' thecharacteristicsspecified in the'precedinglparagraph is used in an'electric blasting cap'in the manner illustrated in F ig. ll, whereinthe'blasting cap consists of aftube shell E formed of brass, copper voialuminum within whichthe 'delay element isiitted betweenA adetoiiatingAcompou-nd F intheY 'bottom of the shell an'dvanignition headG fittedLinto the 'outer end-ofthecap. The primingt composition 'Dv ofthe delay element is spaced from' theelectricy ignition head g Aof theignition head, and the shell between said element-s isl` for-medfwith'openings e which provide vents Vfor the gases formed 'in `the burningof the fuse. F or ig'niting the composition g of the ignition head, apair-ofelecti'ic conductors g joined by a platinum bridge extend throughinsulating materialg'gfof the ignition head. F or protecting'theignition head 'g and-the prim- -it will-be apparent that I have devisedanovel type of safety fuse which may be used in' a conventional mannerand whicliisparltici'ilarly' useful "in the preparation of delayelements for electric blasting caps.

T hese delay elements can be cheaply and accurately -inadefandprovideaneflicient means of increasing the efficiency of the electric blastingcaps ofthe type wherein delayed or properlytimedexplo'sions can beelectricallyfsct off.

Vhile I have shown and described what I consider a preferred embodiment'of-my invention and 'the manner in which 'the sainemay be used, I doVnot wish to be limited-to the specfic construction or composition ofelements described, since these may be varied'within the scope of oneskilled in tlieart without departing from the spirit of my'in'vention.

What I claim is:

l. A Ifuse element consisting of a core" of slow burning powder,cellular material enclosing the powder anda covering of a relativelynon-combustible rigid impervious material snugly engaging over thecellular material, said impervious material having an'accurately sizeduniform external diameter.

2. A fuse element consisting of 'a core of safety fuse enclosed 4withina ductile tube which is drawn down snugly against 'the onter'surfaceofthe safety fuse to reduce to a 'minimum Vairspaces between the fuseand the inner wall of the tube, said ductile tube having an accuratelysized external diameter.

The method of forming a fiise element comprising. enclosing safety "fusewithinan imperforate relatively nonecombustible, rigid, imperviousmaterial, causing said material to `snugly engage over `said safety fuseand accurately and uniformly sizing4 the' outerdiameter of the enclosingmaterial.

t. The method offorming a fuse element comprising enclosing safetyfusewithin an imperforate ductile metal tube aiid then reducing thediameter of the metal tube to lit snugly over the safety'fuse,

For use in blastingV caps or the like, a delay element comprisingalength of safety fuse enclosed throughout' its length in afcasing' ofrelatively non-combustible, rigid, impervious material, the outerdiameter `of which isacciirately sized, one end of the fuse being primedwith an easily ignitable compound.

6. For use in blasting caps or the like, a delay element comprising alength of safety fuse enclosed throughout its length in a ductile metaltube having a uniform external diameter, the fuse at one end of the tubebeing primed with an easily ignitable compound.

7. The method of forming delay elements for blasting caps or the like,comprising forming in long lengths, a fuse element having a core ofinflammable material, a coating of fibrous material enclosing theinflammable material and an outer coating of impervious relativelynon-combustible rigid material, cutting said fuse element into desiredlengths and priming one end of each length so obtained with an easilyignitable compound.

8. The method of forming delay elements for blasting caps or the like,comprising forming in long lengths, a fuse element having a core of slowburning powder, accating of textile material enclosing the powder and ametal covering snugly engaging over the textile material, cutting saidfuse elementA into desired lengths and priming one end of said lengthsof fuse element with an easily ignitable compound.

9. For use in an electric blasting cap comprising a shell having anignition head at the top and a detonating compound at the bottom, adelay element for positioning between said ignition head and saiddetonating compound, said delay element comprising a short length ofsafety fuse snugly enclosed within a metal jacket which is adapted toclosely fit the interior of the shell, said delay element being primedat one end with a compound adapted to be ignited by the ignition head ofthe blasting cap.

10. A delay element comprising a core of inflammable material enclosedwithin a ductile metal tube, and means between the inflammable materialand the tube for preventing the melting or rupturing of the tube duringthe burning of the inflammable material.

ll. The method of Jformingl delay elements for blasting caps and thelike, comprising forming in long lengths a fuse element having a core ofinflammable material enclosed within a ductile metal tube, and meansbetween the inflammable material and the tube for preventing melting orrupturing of the tube during the burning of the inflammable material andcutting said fuse element into desired lengths.

In .witness whereof, I have hereunto signed my name.

HENRY E. ELLSVORTH,

